This invention relates to a flexible inspection system for use in both industrial and medical applications and, more particularly, to an elongated, flexible, fiber-scopic inspection device having an articulating vertebrae assembly disposed along a flexible stiffening member.
It can be readily appreciated that the capability to inspect the internal cavities within a complex mechanical structure, without requiring the disassembly of the structure, is a valuable feature of an inspection system. One such mechanical structure is a jet engine. The use of a flexible inspection device allows for the internal inspection, on a routine basis, of those areas of the engine that are most susceptable to wear and fatigue. The rotor and stator blades within the high temperature first stage of the engine is one such area. Regularly scheduled, routine inspection of the first stages of the engines of a jet aircraft can detect a deteriorating component before such a component fails with a potentially catastrophic loss of human life. If it were required to disassemble the engines each time they were to be inspected, such inspections would, for obvious economic reasons, not occur as frequently.
Another highly valuable application for a flexible inspection device is in the diagnostic evaluation of various cavities within the human body. The colon is such a cavity where a form of the device, known generally as an endoscope, is utilized by physicians to examine the inner walls for abnormalities. Typically, the physician peers through an eyepiece located on a control mechanism while manipulating control knobs, thereby guiding the probe tip while advancing it through the colon and simultaneously examining the inner wall thereof. The eye piece is located at the proximal end of a fiber-optic bundle, the bundle typically being enclosed within a flexible tube. The distal end of the flexible tube terminates in an objective head. Cables connected to the control knobs extend through the flexible tube to the objective head. The manipulation of the control knobs varies the tension within the cables, thus effectuating a lateral movement of the distal probe end whereby the distal end can be guided through the convolutions of the lower bowel. Also enclosing within the flexible tube are, typically, one or more additional fiber optic bundles for the purpose of illuminating the area being viewed, the source of the illumination being a lamp coupled to the proximal end of these bundles. If desired, the endoscope can further incorporate a channel for conveying a washing solution to the distal end, as well as a surgical tip and other useful features.
The industrial corollary of the endoscope is typically known as a borescope, an application for which was described above as an inspection instrument for jet engines. The construction principles of both instruments, namely the endoscope and the borescope, are similar. The differences between the instruments typically being in the dimensions of the flexible tube and the nature of the protective sheath covering the tube. For instance, the flexible tube of a borescope may be required to be enclosed within a jacket of metal braid or some similar rugged material, while such a sheath would be inappropriate for use with an endoscope.
As may well be appreciated, an important component of a flexible inspection instrument is the region adjacent to the distal end where the articulation of the objective head is effectuated. Such a region is typically comprised of the objective head, wherein the optical elements and the control cables terminate, an adjacent chain of articulating vertebrae, which provide for precisely manipulating the objective head, and a coupler whereby the chain of articulating vertebrae are coupled to the flexible tube. In the past various methods of interconnecting the individual articulating vertebrae have been devised, the goal of each method to provide an articulating member capable of precisely controlled movement, flexibility, and structural strength and integrity.
One typical method to accomplish these goals is to join adjacent vertebrae together with pins, the vertebrae being shaped such that they may pivot relative to one another about the pins. Illustrative of such a prior art joining technique are U.S. Pat. Nos. 3,799,151, and 4,530,568, said last U.S. Patent assigned to the assignee of the present invention. The method of joining the vertebrae shown and described in the above mentioned prior art, while suitable for forming a chain of articulating vertebrae, is also disadvantageous for several reasons.
One problem arising from such a pinning method is that a complicated and costly assembly procedure is required to pin each vertebrae to the two adjacent vertebrae, due to the small size of both the vertebrae and the pins, and to the number of vertebrae required to be joined, a typical value being 18 or more.
Another problem with this type of prior art joining technique is that a lower design limit is reached on the size of the individual elements. As the physical dimensions of the vertebrae and pins are scaled down for small caliper assemblies, the assembly procedure becomes even more difficult and costly.
Another disadvantage of the prior art method of joining the individual vertebrae by pinning results from each pivot point having a characteristic amount of friction associated with it. The friction characteristics of each pivot point are typically different from one another, the difference being due to the normal physical tolerances of the individual elements. Thus, a differing degree of articulation may be present in various regions along the chain of vertebrae, resulting in a non-uniform curvature of the articulating vertebrae assembly.
Another less obvious problem with this prior art joining technique is that as the number of individual components, represented by vertebrae and pins, of the chain of articulating vertebrae increases, the overall reliability decreases as there is an increased probability of individual component failure.
To overcome these problems it has been known in the prior art to join the individual vertebrae together with two or more wires of small cross-sectional diameter which are threaded through holes made longitudinally through the vertebrae. Illustrative of this prior art joining method are U.S. Pat. Nos. 3,190,286 and 3,557,780. U.S. Pat. No. 3,557,780, to M. Sato, which patent is incorporated herein by reference, describes a mechanism for controlling the flexure of an endoscope wherein articulated segments have opposing faces tapered to form diametrically extending pivot ridges. The pivot ridges are flexibly urged together by two wires, one of each of the wires passing through two diametrically opposed small holes which are provided through the segments at positions in the pivot ridges. U.S. Pat. No. 3,190,286, to R. Stokes, which patent is also incorporated herein by reference, discloses a flexible viewing probe comprised of segments having holes disposed 90 degrees apart, pivot elements interposed between the segments, and a control wire or cord passing through each hole and pivot element whereby the probe may be controllably flexed by the movement of the segments about the pivot elements.
The aforementioned prior art method of joining the vertebrae by the use of two or more wires, although embodying a simpler mechanical principle than the aforementioned method of pinning adjacent vertebrae together, suffers from the problem that the probe may experience an undesirable torsion or twist about its longitudinal axis. Such a torsion may occur when the probe body or objective head is subjected to a tangential force, such as may be encountered in the complex movements the device makes within the cavity being inspected. The tensioning forces imparted by the control cables may also cause the probe body to undergo a torque, if such tensioning forces are unbalanced either by design or inadvertently during operation. This susceptibility to torqueing forces, resulting in an undesirable torsion about the longitudinal axis of the probe tip, is due to the tendency of the internally disposed joining or control wires to twist about their longitudinal axis when subjected to a torque.
It has also been known in the prior art to join the individual vertebrae together by the use of a pair of flexure strips which are secured to spaced apart vertebrae by welding, cementing, or tongue and groove means. Illustrative of such a method is U.S. Pat. No. 2,975,785 to G. Sheldon, which patent is herein incorporated by reference.
One disadvantage of this method is that because the flexure strips are rigidly secured along each of the vertebrae, that the flexure must occur in that portion of the flexure strips between adjacent vertebrae. Thus the stresses due to bending which are induced within the flexure strips are localized to those regions between vertebrae, rendering the flexure strips more susceptable to stress induced cracking and failure.
Another problem with this prior art method is that the overall degree of curvature of a given length of such a vertebrae assembly is limited to that which can be accomplished within that portion of the flexure strips not rigidly attached to the vertebrae. All of the flexure must, therefore, occur in that region of the flexure strips between adjacent, spaced apart vertebrae. As may be realized, if a greater degree of curvature is desired, the overall length of the vertebrae assembly so joined together must be made correspondingly longer, which in some applications may not be practical.